The present invention relates to a method of forming a substantially regular array of microscopic structures on a substrate. The invention relates particularly, but not exclusively, to a method of forming nanometer sized wire-like structures on a substrate.
Methods of imposing patterned surface structures on articles have applications in the fabrication of various devices, for example data storage media, microelectronic and micro-electromechanical devices, sensors, optoelectronic display devices, and other optical and optoelectronic components such as optical components for directing atomic beams, as well as applications in tissue engineering and for cell adhesion or non-adhesion, or for guiding motion or growth of cells, liquids or molecules, or in molecular scale filters. Known patterning processes involve optical lithography processes or direct-write patterning techniques such as electron beam lithography and scanning probe methods.
However, optical lithography processes suffer from the drawback that they are of limited resolution, and direct-write patterning techniques, although capable of achieving higher lateral resolution than optical lithography, are impracticable for use in mass production applications because the serial nature of the surface modification process is inherently slow. Also, when applied to larger areas of material, for example more than a few square centimeters, such processes suffer poor large scale dimensional accuracy, and in the case of patterning formed by step and scan techniques, poor registration between separate write operations and scanned regions is achieved.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
According to the present invention, there is provided a method of forming a substantially regular array of structures on a substrate, the method comprising:
providing a surface layer of a first material on a substrate of a second material, wherein said surface layer is sufficiently thin that stress fields at the interface of said surface layer and said substrate cause formation of separated regions of said first material on said substrate; and
directing at least one first particle beam onto said surface layer and at a respective acute angle thereto to influence the direction of alignment of said separated regions and/or the relative position of adjacent said separated regions.
By directing at least one first particle beam onto the surface layer to influence the direction of alignment of said separated regions and/or the relative position of adjacent said separated regions, this provides the advantage that nanometer-scale structures having a high degree of regularity can be formed on the surface. Structures having such a high degree of regularity have a number of technical applications, and can either not be formed using conventional techniques, or can only be formed at significantly greater cost and/or complexity.
The step of providing said surface layer may comprise depositing said layer on said substrate.
In a preferred embodiment, said surface layer is deposited by means of at least one second particle beam.
The step of providing said surface layer may comprise modifying the surface of said substrate by means of at least one particle beam.
In a preferred embodiment, the surface of said substrate is modified by means of at least one said first particle beam.
This provides the advantage that the surface layer from which the structures are to be formed can be formed at substantially the same time as the formation of the substantially regular array of structures, by carrying out both steps by means of the same particle beam or beams.
The method may further comprise the step of adjusting the direction of at least one said first particle beam relative to said surface layer.
This provides the advantage of enabling the nature and/or formation of the substantially regular array of structures to be adjusted.
The adjustment step preferably comprises rotating said surface layer relative to at least one said first particle beam.
The method may further comprise the step of moving at least one said first particle beam relative to said surface layer.
Said step of moving at least one said first particle beam preferably comprises scanning at least one said beam across said surface layer, or moving said surface layer relative to at least one said first particle beam.
The method may further comprise the step of mounting said substrate to an earthed support.
This provides the advantage that under certain circumstances, at least one said particle beam may impact on the earthed support, which may result in at least partial neutralisation of any electrostatic charge building up on the surface layer or on the substrate.
The method may further comprise the step of stabilising said substantially regular array of structures.
In a preferred embodiment, said stabilisation step includes the application of at least one protective coating.
In another preferred embodiment, said stabilisation step includes chemical modification of said substantially regular array of structures.
The method may further comprise the step of at least partially filling at least some gaps between adjacent said structures of said substantially regular array.
In a preferred embodiment, said step of at least partially filling at least some gaps comprises adsorbing at least one gaseous material into material in said gaps.
The step of at least partially filling at least some gaps may comprise depositing material into said gaps.
The method may include directing at least two said first particle beams onto said surface layer, wherein at least two said first particle beams are not parallel to each other.
The method may further comprise the step of forming a plurality of said substantially regular arrays of structures.
In a preferred embodiment, at least two said substantially regular arrays of structures are arranged in separate layers.